Cutting material used in a drill member is conventionally tungsten-carbide or the like which has a hardness which is considerably greater than the hardness of tool steel. Therefore, the tungsten-carbide material is excellent cutting material. However, the tungsten-carbide material is very costly compared to the cost of tool steel material.
In the past, efforts have been made to reduce the volume of costly tungsten-carbide material or the like used in a drill. A shank of tool steel is conventionally used to support at the end thereof an elongate generally cylindrical body of tungsten-carbide material, which is brazed to the end of the shank. There have been other attempts to reduce the volume of costly cutting material at the end of a drill shank. However, in all of these attempts the volume of the costly cutting material has been greater than necessary for proper functioning of the drill, or the cutting material provided at the end of the shank has not been properly shaped or sufficient in volume or has not been appropriately located for best functioning of a drill.
Thus, it is an object of this invention to provide a drill which contains a minimum volume of costly cutting material but which contains sufficient cutting material for proper functioning of the drill.
It is also an object of this invention to provide a drill in which a minimum cutting web is provided for best centering operation of the drill.
Other objects and advantages of this invention reside in the construction and arrangement of parts, the combination thereof, the method of manufacture, and the mode of operation as will become more apparent from the following description.